1. Technical Field
The present invention relates to methods of producing hydrocarbon fluids from a subterranean well, using stem injection.
2. Background Art
In some areas of the world, there are large deposits of very viscous or heavy crude oils, in formations, such as shale and tar sands. One especially effective technique used in the past for producing such heavy tar or oil sand formations has been steam flooding of the formation. In steam flooding, a pattern of wells is drilled vertically through heavy oil bearing formation. Casing is put in place and perforated in the producing interval and then steam generated at the surface is pumped under relatively high pressure down the casing and into the formation. In some instances the steam may be pumped for a while into all of the wells drilled into the producing formation and, after the heat has been used to lower the viscosity of the heavy oil near the wellbore, then the steam is removed and the heated, lowered viscosity oil is pumped to the surface, having entered the casing through the perforations. When the heat has dissipated and production falls off, the production is closed and the steam injection is resumed. Where the same wells are used to inject steam for a while and then are used for production, this technique has been known as the huff-and-puff method or the push-pull method. Production from this single well is limited by the penetration of steam in the formation around the wellbore.
In other instances, multiple wells penetrating the heavy oil bearing formation are used to continuously inject steam, while others are used to continuously produce lower viscosity oil heated by the steam. This multiple well method can result in larger and more efficient production of heavy oil but involves the increased costs of drilling multiple wells. Again, when production falls off due to lack of heat, the role of the injectors and producers can be reversed to allow injected steam to reach new portions of the reservoir and the process repeated.